( «55 ) 
ufed, except when the Angie to be obferved is very 
fmall. The chief Inconvenience will be, that a finall 
Star will be more difficultly difcerned, the Light be- 
ing divided among the feveral Images. The Teiefcope 
may be contrived to alter its Situation, fo as to re- 
ceive the reflected Rays on a greater or lefs Part of 
its Objeft-Giafs, if the Objefts differ in Brightnefs. 
The fecond Speculum may have a Part unfoil’d, that 
if either of them be fufficiently luminous, the lefs 
bright may be feen through it by the whole Aperture. 
If the Sun be one of the Objefts, or the Moon be 
compared with a fmaller fix’d Star ; their reflected 
Images muft be ftill farther weakened by the Inter- 
polation of one or more of the dark Glaffes S T. An 
exaft Pofition of the Teiefcope is not necefiary; and 
the Inftrument may be ufed without one, the Difpo- 
fition of the Specula, with regard to the Seftor and 
Index, being fuch as may allow the Eye to be brought 
as near the fecond Speculum as may be, and make the 
Inftrument the moft commodious for the Obferver. 
It will be eafy to judge, that fcarce any greater De- 
gree of Steadinefs is requifite in the Pedeftal, or Ma- 
chine which carries this Inftrument, than what isfuf- 
ficient for the Teiefcope us’d with it : For although 
the vibrating Motion of the Inftrument may occafion 
the Images of the Objefts alfo to vibrate crofs one 
another ; their apparent relative Motion will be very 
nearly in Lines parallel to cf\ and it will not be dif- 
ficult to diftinguifh whether they coincide in crofling 
one another, or pafs at a Diftance: And if the Ob- 
jefts are near one another, and the Teiefcope mag- 
nify but about four or five Times, it may be held in 
X the 
